The present invention relates to an implantable multi-lumen multi-conductor lead for use with an implantable medical device.
Medical leads are used to transmit electrical signals to and from medical devices such as pacemakers. The lead body is usually made from a piece of polymeric tubing having a round cross-section exterior and a round cross-section lumen. Typically a coiled metallic electrical conductor having a round cross-section is placed in the lumen completely filing it. The tubing protects and insulates the conductor. The coiled conductor can usually receive a stylet to help position and place the lead during implantation. Such a lead is illustrated in U.S. Pat. No. 3,348,548.
Since both the conductor and lumen have a round shape with substantially equal diameters, assembly of the lead can be difficult due to friction between the conductor and lead. Because the lead body is flexible, and the conductor coils are substantially more rigid, this problem is not substantially reduced by the use of circular lumens slightly larger in diameter than the coils. In areas where the lead body is flexed, the result is still that the lumen wall will deform to contact a substantial percentage of the circumference of each individual coil. Assembly problems are exacerbated when this form of lead construction is extended to small diameter, multi-conductor, multi-lumen designs.
Various alternative designs have been proposed to form multi-lumen leads. U.S. Pat. No. 4,608,986 discloses a lead having an array of round lumens, but using essentially straight, uncoiled conductors. Multi-lumen tubing having non-round lumens is known in the art. See for example the advertisement by Putnam Plastics Corporation in the July/August 1990 issue of Medical Product Manufacturing News. For example, multi-lumen tubing having pie-shaped lumens is used to manufacture thermodilution catheters, which may include a twisted wire pair in one of the lumens, connected to a thermistor.